The continuous shrinking in dimensions of electronic devices utilized in ULSI circuits in recent years has resulted in increasing the resistance of the BEOL metallization as well as increasing the capacitance of the intralayer and interlayer dielectric. This combined effect increases signal delays in ULSI electronic devices. In order to improve the switching performance of future ULSI circuits, low dielectric constant (k) insulators and particularly those with k significantly lower than silicon oxide are needed to reduce the capacitances.
Most of the fabrication steps of very large scale integration (VLSI) and ULSI chips are carried out by plasma enhanced chemical or physical vapor deposition techniques. The ability to fabricate a low k material by a plasma enhanced chemical vapor deposition (PECVD) technique using previously installed and available processing equipment will thus simplify its integration in the manufacturing process, reduce manufacturing cost, and create less hazardous waste. U.S. Pat. Nos. 6,147,009 and 6,497,963, which are incorporated herein by reference in their entirety, describe a low dielectric constant material consisting of elements of Si, C, O and H atoms having a dielectric constant not more than 3.6 and which exhibits very low crack propagation velocities.
U.S. Pat. Nos. 6,312,793, 6,441,491 and 6,479,110 B2, incorporated herein by reference in their entirety, describe a multiphase low k dielectric material that consists of a matrix composed of elements of Si, C, O and H atoms, a phase composed mainly of C and H and having a dielectric constant of not more than 3.2.
Ultra low k dielectric materials having a dielectric constant of less than 2.7 (and preferably less than 2.3) are also known in the art. The low k and ultra low k SiCOH films can be non-porous, or porous. Porous films are typically formed by introducing a porogen during the deposition of the film, which is subsequently removed after deposition using a conventional curing process. Generally, porous SiCOH films have a lower dielectric constant than the corresponding non-porous SiCOH films.
A key problem with prior art low and ultra low k SiCOH films is that they have poor mechanical properties (such as, for example, a high crack velocity and stress, and a low modulus and hardness). Typically, the mechanical properties of prior art SiCOH dielectrics deteriorate as the dielectric constant of the material decreases. Hence, porous SiCOH dielectrics tend to have poorer mechanical properties than the corresponding non-porous SiCOH dielectrics.
Improved mechanical properties of low k or ultra low k SiCOH dielectrics can be achieved in the prior art by treating the SiCOH films post deposition. For example, curing or treatment using thermal, UV light, electron beam irradiation, chemical energy or a combination of these energy sources has been used to stabilize the low or ultra low k dielectric material and to improve the mechanical properties of the same. While such post deposition treatments are possible, they add extra processing steps and thus cost to the manufacturing of low k or ultra low k dielectric films.
In view of the above, there is a need for providing porous low k and ultra low k dielectric films which exhibit good electronic and mechanical properties, without the need for post film treatments or introducing a porogen during the deposition process.